Well I guess that's good new because it does swing from 0 to about 0.6v. The reason I asked was - a few months ago I was having some idle and driveability problems that definately seemed engine management related. So i replaced all sensors - coolant temp, TPS, O2, AMM, FPR, AIC as well as all ign tune up stuff, filters, vac hoses, intake vac port bushings, BOV...... you get the point, preventative maintenance and ruling out all causes. I also installed a narrow-band to keep an eye on how things were working. Car ran absolutely perfect in all conditions for a few months. During this time the O2 output and RPM were always rock steady (0.6v and 800rpm warm), without even a slight waver of a needle at idle. Vacuum was also steady at about 23hg when warm. Now about 15K km's later, the O2 swings (like it should I now know), but the rpm has a 600-750rpm range, and the vacuum gage wavers around 18-21hg. I know a C900 isn't known for the smoothest idle, and this might sound rediculous, I'll admit I'm obsessive compulsive about how my car runs. I just want to know the cause of the change in behavior. Why would the O2 not swing at idle when it was new and then a few months later it starts swinging?
I wouldn't blame any of you guys if you don't feel like responding to my rant here But I just had to throw it out there because it annoys me that I can't explain it!! Haha
The O2 sensor voltage is supposed to swing in response to the oxygen content in the exhaust gases. While you may notice it to be "rock steady", it is in fact fluctuating. A digital or analogue voltmeter will not be able to follow the fluctuation, but it is there. After all, the O2 sensor forms part of the closed loop system and the negative feedback from it gives you, in part, the correct idle.
I say "in part" because correct idle is regulated by a number of components, chief of which is the AIC. The O2 sensor's primarily job is for emissions control, not idle. In other words, I think the O2 sensor is a red herring.
I would check the AIC by simply removing the AIC valve and spraying it with carb cleaner at both ends. Depending on how gunk-y is the screw valve, you may not have to disassemble it (there are reports of AIC valves being cleaned so thoroughly that the valve can't close entirely, causing a high idle).
Replaced the AIC with a brand new one. Could be that it is getting sticky already though - I'll try cleaning it. My perception of a steady vs a swinging output from the O2 is based on the reading I get from my narrow-band air/fuel gauge, which just basically displays the O2 reading. And I think I can rule out a vacuum leak if there's no increase in idle rpm (actually a bit of a decrease) can't I?